Method of making trimetallic plate



Patented Oct. 29, 1940 PATENT OFFICE 2,219,957 METHOD OF MAKINGTRMETAIJJC PLATE Howard J. Kerr, Westfield, N. J., assignor to TheBabcock & Wilcox Company, Newark, N. J., a corporation of New Jersey 7No Drawing. Application May 9, 1936,

Serial No. 78,857

1 Claim.

This invention relates to a metal article, and the method of making it,wherein the metal of one face has physical and chemical properties 5different from those of an opposite face capable of use under conditionsfor which the properties of either one would be unsuitable. In one ap-vplication of the invention the article may be a metal plate, the majorthickness of which has one set of properties and the minor thicknessanother set, but with a transition zone as to properties makingseparation impossible and making the plate a unitary structural elementin resisting use forces.

The invention is especially suitable as an element of a stressedstructure subject to corrosion influences on a face, particularly suchas the wall of a pressure vessel to contain corrosive chemicals, andmore particularly when subject to changes of temperature in use,inaddition the stresses due to pressure and the internal face corrosion.

Metals resistant to corrosion or attack by various chemicals of acid oralkaline character are well known but many of them are of high cost, andmay be otherwise unsuitable as stressed members in large structuressubject to variable temperature, and numerous attempts have heretoforebeen made to provide an article having a face of such metal on the sideor sides subject .to attack, and with a foundation body of lessexpensivematerial and suitable otherwise for the desired structure.

One such attempt isapparent in the United States patent to A. E.-Gillespie 1,306,690, issued June 1'7, 1919, wherein chrome alloy steeland mild steel are united by rolling, hammering or forging when hot.Another process or method is that wherein a clad plate is formed withcorrosion resistant material on one side by first forming a. sandwich oftwo corrosion resistant alloy plates permanently separated by a suitableintervening compound, casting base metal on either side of the sandwich,rolling a billet 5 thus formed into plate thickness at a forging heat,separating it at the original permanent division between the alloyplates and thus arriving at two sheets, each composite with itsrespective cladding of corrosion resistant metal. 50 By" still another\method a sandwich is formed from a low priced steel base metal and analloy cladding metal with an intervening thin uniting sheet of lowcarbon steel; the peripheral edges of the sandwich are then first unitedby fusion 55 welding and the whole then rolled under forging heat andpressure until a composite plate is formed.

However, all of these clad plates made by the methods heretofore knownhave failed in use by 5 local ruptures of the bondbetween the claddingand the base metals with consequent deterioration and lossof utility.The present invention does not fail in service and retains its utilityindefinitely because it is an integral metal mass which while diiferentas to properties on opposite faces is insured, by the method of making,against too abrupt a change in these properties in a juncture zone,earlier ones having failed because one metal composition changed to the15 other too abruptly without an adequate transition zone.

Another object is to select two different metals of such commensuratephysical, chemical and other metallurgical properties, for example one20 for resisting stress, and the other for resisting corrosion, thatwhen combined according to this invention a tough, ductile product'witha minimum of local stress at the junction is the result, whereby, insubsequent working, forming and 25 the like, or in service, there is noseparation or cracking of the one with respect to the other due to localover-stress failure.

, A further feature of this invention is that the different metals areso selected and combined 30 originally that subsequent rolling actionunder heat only serves to increase the integrality of the union betweenthe different-metals, and to preserve the width of the transition zonesuflicient to avoid local stresses that the metal carriers 35 resist,especially those due to unequal expansion.

Additionally, by reason of the method employed, the amount of expensivecorrosion resisting metal used for the surfacing of the article is muchless than with, other methods due 40 to the fact that rolling toultimate form may be carried to such an extent, by reason of theintegrality of the bond and consequent lack of stress at the junctionwith elimination of liability to cracking and separation, that the finalcladding may be of only just suflicient thickness of the cladding metalas to afford resistance to chemical action.

Another feature of the invention is the uniting of the different metalsat a temperature for each which represents superheating the same,namely, a temperature above the melting point and under conditionsproducing a junction free of porosity and non-metallics initially in themolten state at the junction.

In. executing the method of the invention one article which may be made,and from which other articles may then be formed, is a fiat plate havingone face of one metallic composition and the opposite face of anothermetallic composition with a gradation at the juncture between thedifferent metals of the composition and properties of the metal of oneface to the composition and properties of the metal of the other face inthe zone between the two faces, and which holds true whether oppositefaces are of like or different metals and the depth of which gradationzone is never zero but always ade- (mate to avoid such excessive localstresses as .might cause fracture.

A feature of the invention is the combination of different metals intoan integral plate such that the gradation of metals and thecorresponding gradation of physical properties, like coefficients ofexpansion, are so related as to avoid locally high concentration ofstresses, a condition which accounts for the disintegration of the unityof the hereinbefore referred to composiiie plates and cracking of theresistant metal. In detail, the invention, irrespective of the differenttypes'of metals combined, embraces the selection of a starting orfoundation piece of base metal of adequate size and thickness for theultimate article, which ultimate article in the present instance I shallassume to be a finished plate of metal to be protected on one side witha resistant metal suitable for the wall of a pressure vessel, and theselection of a resistant alloy, of commensurate physical and chemicalproperties to resist corrosion attack of the vessels contents, for.fusion welding-thereto.

Upon the face of the foundation piece or base metal there is deposited acoextensive covering of the corrosion resisting metal, the deposit beingmade by fusion welding, preferably with the electric arc, and preferablyfrom a bare electrode haps advantageously before the first have had anopportunity to cool below a critical tempera- 55 ture. -With somemetals, and with some sizes of electrodes and currentvalues for the rateof deposit' employed, it has been found desirable to maintain the wholebase metal plate in a heated condition but below fusion temperature.

creased solution of the one metal into the'other when the face of thebase metal plate is locally melted by the arc and in contact with moltenweld metal. Other possible causes of the bene- 65 ficial result arelessened surface tension, 8. consequent spreading of the deposited metalover a larger area for each bead, a higher rate of deposit for lowercurrent densities and less irregular biting into the base metal, and aminimum 70 vaporization of metal. In all instances the weld metaldeposit is so made that there is a superheating of the metals at thejuncture with consequent solution of the one into the other to thedegree necessary for union: and a gradationzone 75 of sufiicient depthto avoid rupture stresses is The 60 beneficial result is believed to bedue to an informed. The term superheating as here used means heating toa temperature in excess of that at which melting occurs and at whichtemperature the metals themselves are both molten at the zone ofcontact, the weld metal being wholly melted, and the base plate metalmelted only at the welding face for a limited depth.

One specific manner in which the invention has already been carried intopractice, but which is only one of many which I consider within thescope of the invention, is as follows:

An 8" x 8" carbon steel billet (carbon range 0.18 to 0.25%) was rolledinto a plate 4%" thick.

A section 60" long x 9'-' wide x 4%" thick was cut from this billet andmachined on one side in orderto clean it up for fusion deposit of metalthereon.

The plate was then heated to approximately 1000 F. and layers ofresistant weld metal of the following composition were fusion arcdeposited in parallel intersecting beads on the machined surface, carbon.10'max., manganese .75 max.,

, silica .50 max., chrome 17.0 to 19.0; the plate was maintained at aminimum temperature of 900 F. at all times during the welding.Deposition of the weld metal on the heated plate was by the metal aremethod, using electrodes having a covering or coating producing anenvelope of reducing gas shielding the arc.

When the welding had been completed the thickness of the alloydeposition was A" to which required three bead thicknesses in depth.

Immediately after welding the resulting plate was heat treated at 1450F. followed by furnace cooling. The alloy side of the plate was thensand-blasted and defects removed by grinding and re-depositing wherevernecessary.

The plate was then rolled hot at a forging temperature and thus reducedin thickness from 4%", plus the thickness of the alloy deposited, to afinished rolled thickness of /3" and a total outside dimension of 8 ft.long x 3 ft: wide; the reduction in thickness from the. original alloyclad plate being 87'/ with an alloy thickness ranging between .03" and.04", with no cracks through the alloy, and a quite apparent solution ofthe one metal into the other at the junction, thus producing agradation, however thin, at the junction, from the metal of one face tothe metal of the other in the intermediate zone.

As previously stated the weldrods usedin deposition contained 17.26% ofchromium and a sample section of the deposited alloy n analysis showedthe following:

Carbon Manganese Silicon Chromium It is to be noted that there was aloss of 4% chromium from weldrod to deposited weld metal due, in part,to oxidation, and in part to dilution with steel at the juncture. Theplate described was made by a hand method of deposition withconsequently wide variations in the arc length,.

whereas itis a part of this invention to deposit this weld metal by theautomatic arc method in ing of the metals at the junction.

The finished plate may be subjected to another heat treatment forannealing if desirable.

At the junction between the weld deposited metal and the steel of thisplate described there is perfect fusion throughout and freedom from nonmetallics. Decarburization of the carbon steel in the juncture is due toa migration of the carbon into the higher chromium region. Physicaltests demonstrated that when a 15" x 6" sample of this plate is heatedto 950 F. and held there for a minimum period of one hour and then waterquenched, this being repeated for 18 times, and a similar sample sotreated and air quenched 9 times, there is no indication ofanyseparation between the alloy surface and the body steel, and no growthor cracking of the alloy occurred.

The heating of the base metal or foundation plate may be performed inany suitable manner as for instance, by induction currents, and in somecases it may, advantageously, even be carried to the degree ofplasticity of the metal, or it may be eliminated altogether.

With plate made according to the method of this invention there is notendency to curl after' the final rolling, as is thecase with compositeplates of the character referred to in the forepart of this description.

While, in the foregoing, I have described the invention asto one methodof practicing it to produce the article, it is nevertheless to beconsidered that what is claimed as new is the combination of methodsteps by which an integral resistant clad metal plate is produced asagainst the composite plates known in the prior art, and

I also claim as new the article made by such method.

I claim:

The method of forming a metal plate which consists in starting with abase metal plate and a surfacing metal each having differentmetallurgical properties, dissolving the surfacing metal onto thesurface of the plate by the electro-fusion well depositing of thesurfacing metal to form an al- 10y, permitting the alloyed surfacematerial to freeze, successively repeating similar depositions of layersof the surfacing metal, with intermediate freezing until the surfacelayer is built up and diluted to substantially the purity of thesurfacing metal, then stress annealing the tri-me-- tallic plate thusformed and pressure reducing the plate to a selected area and thicknessof the different metals, and then again stress annealing the plate.

4 HOWARD J. KERR.

